|[AMRadio] Local oscillators and TVI|
Jim Miller WB5OXQ
wb5oxq at grandecom.net
Sun Mar 5 11:52:22 EST 2006
When I was in high school in the mid 60s a friend bought a older multiband
console radio, RCA model 15K built in 1937.
This was a real good sounding console with a tuned speaker compartment
housing a 12" EM speaker which must have weighed 30 pounds. The receiver
had 15 tubes and push pull 6L6 output so it was healthy to say the least.
The most interesting band was in the 40-60mhz range which could pick up the
highway patrol broadcasts. I now know that was probably supposed to be the
original FM band that was before they moved it to 88-108mhz. Anyway those
radios had no internal antenna and needed a piece of wire attached to the
antenna terminal for best reception. We found that an old outdoor tv
antenna worked real well for reception on the fm band. I would visit at
this home at night after supper and we would listen to the police calls for
a long time. We soon began to notice the neighbors would have the mobile tv
repair truck at their house regularly. I wandered over to listen to the
conversation the neighbor was having with thje tv repariman as he was
leaving their house. It seems that their tv played well in the daytime and
the repariman could find nothing wrong but ths neighbor told him that after
the evening news, they could barely pick up any stations at night (using
rabbit ears). That is when we learned about local oscillators. Since there
were no tv sets in 1937 and probably no FCC regulations about harmful
radiations the set was a real good transmitter on the low band channels.
Our local NBC station was channel 3. I guess using a tv antenna for an
external antenna on the old RCA really helped make the transmitted signal
even stronger! We found that funny and made a paper label and gluded it to
the back of the radio stating that "This receiver DOES NOT conform to part
Later we built a AM broadcast transmitter using a single 6L6 but that was
short lived and we never got caught.
Jim in Waco, WB5OXQ
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